Live: View as Super Hurricane Irma moves over the Caribbean

Monster Hurricane Irma hammered the Caribbean island of St. Martin on Wednesday as it packed a potentially catastrophic mix of pounding winds and rain and surging surf that was expected to make landfall in Florida over the weekend.

Irma could become the second powerful storm to thrash the U.S. mainland in as many weeks, but its precise trajectory remained uncertain. Hurricane Harvey killed more than 60 people and caused as much as $180 billion in damage after hitting Texas late last month.

Martin, the National Hurricane Center (NHC) in Miami said. Category 5 is its highest category.

Its trajectory indicated Irma, which the NHC said was the strongest Atlantic storm on record, would skirt most of the Caribbean as it moves west-northwest.

Karel van Oosterom, the Netherlands ambassador to the United Nations, said Irma hit the Dutch islands of Saba and Sint Eustasius before overrunning St. Martin.

"First information indicates that a lot of damage has been done, but communication is still extremely difficult," he said at a U.N. meeting.

Irma began lashing Puerto Rico with rain at mid-morning. Governor Ricardo Rossello told residents to stay inside as the storm bore down on the island. “There is no reason to be in the street,” Rossello told a midday press conference.

Many businesses in San Juan, the island's capital, were closed and many buildings were covered with storm shutters. Occasional shoppers were out making final purchases of water, ice and food to prepare for what could be several days without power.